The present invention relates to network interfacing, and more particularly, to methods and systems for calibrating physical layer transceivers configured for receiving network signals carrying data between network stations connected to a telephone line.
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.
Conventional local area network architectures use media access controllers operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) protocol using a prescribed network medium, such as 10 BASE-T. Newer operating systems require that a network station to be able to detect the presence of the network. In an Ethernet 10 BASE-T environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10 BASE-T media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based on detection of the periodic link pulses. Hence, a PHY transceiver at Station A is able to detect the presence of Station B, without the transmission or reception of data packets, by the reception of link pulses on the 10 BASE-T medium from the PHY transmitter at Station B.
Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10 BASE-T. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment. However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak-to-peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmit clock or transmit data from the received pulse becomes substantially difficult.
Hence, a physical layer transceiver for a home network environment must be able to precisely detect, amplify, and decode the network signal with precise signal processing circuitry. However, implementation of a physical layer transceiver in silicon results in additional problems related to the accuracy and precision of the receiver circuitry. In particular, uncertainties in process variations during manufacture may be a potential source for offset errors between independent circuits in the physical layer receiver, consequently effecting the detection of the smaller network signals having peak to peak voltages on the order of 10 to 20 millivolts.
There is a need for a network station having a physical layer transceiver capable of reliably recovering data from a received network signal on a telephone line medium.
There is also a need for a network station capable of self-calibrating its physical layer receiver circuitry to minimize errors due to process variations during manufacturing.
There is also a need for an arrangement in a physical layer transceiver for selectively calibrating a receiver by determining an optimum common mode voltage signal relative to minimum noise thresholds.
There is also a need for an arrangement in a physical layer transceiver that enables efficient calibration of signal generator circuits having matched circuit design and layout structures.
These and other needs are obtained by the present invention, where a physical layer transceiver in a network station is configured for automatically calibrating a receiver circuit based on a correlation between a common mode voltage signal having a selected value, and a predetermined noise threshold. The common mode voltage signal is supplied to the receiver circuit, and a comparison is made between the common mode voltage signal and the prescribed noise threshold. The common mode voltage signal is selectively set to a calibrated value based on the determined presence of an event where the common mode voltage signal falls below the prescribed noise threshold.
According to one aspect of the present invention, a method of calibrating a physical layer transceiver, configured for receiving network signals from a telephone line medium, includes generating in a common mode voltage generator a common mode voltage signal having an initial maximum value, and supplying the common mode voltage signal to a receiver circuit configured for processing the network signals from the telephone line medium according to the common mode voltage signal. The receiver circuit includes a noise comparator configured for generating a noise comparison signal based on an input signal exceeding a prescribed noise threshold. The method further includes determining a presence of an event where the common mode voltage signal falls below the prescribed noise threshold as the input signal, and selectively setting the common mode voltage signal to a calibrated value based on the determined presence of the event. The generation of the common mode voltage signal having an initial maximum value provides an efficient arrangement for determining where the common mode voltage signal falls below the prescribed noise threshold, since the common mode voltage signal can be successively reduced until the common mode voltage signal falls below the prescribed noise threshold, indicating that the common mode voltage signal can be set to the calibrated value. The calibrated value thus provides an optimum common mode voltage signal for use in the receiver circuit for processing the network signals. Moreover, the determining of the event where the common mode voltage signal falls below the prescribed noise threshold as the input signal provides precise calibration relative to an internally-controlled signal, without introducing any variations that may be otherwise encountered by using an external reference signal during calibration.
Another aspect of the present invention provides a physical layer transceiver configured for receiving network signals from a telephone line. The physical layer transceiver includes a digital to analog (D/A) converter for selectively generating a noise threshold signal based on a supplied threshold value, a common mode signal generator for selectively generating a common mode voltage signal in response to a common mode selection signal, and a receiver circuit configured for processing network signals from the telephone line medium according to the common mode voltage signal. The receiver circuit includes a noise comparator configured for generating a noise comparison signal in response to an input signal exceeding the noise threshold signal. The physical layer transceiver also includes a calibration control circuit configured for determining a calibration setting for the common mode signal generator based on the noise comparison signal, the calibration circuit setting the common mode selection signal to an initial maximum setting and selectively reducing the common mode selection signal to the calibration setting based on a determined presence of a transition in the noise comparison signal relative to the minimum noise threshold signal.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.